Electronic devices, such as integrated circuits and microprocessors, require a power supply to operate. In some situations, it may be desirable to have more than one power supply available. Multiple power supplies are routinely connected in parallel for redundancy and in situations where more than one supply are needed to deliver the load current. With parallel supplies, it is desirable to equally distribute load current among the supplies. Otherwise, one or more power supplies may handle more than their respective share of current, thus leaving some power supplies essentially idle. This creates greater thermal stress on some units and reduces the reliability of the system.
Previously developed techniques for using parallel power supplies suffer from various problems and disadvantages. According to some previously developed techniques, current sharing among a parallel power supplies could only be achieved using elaborate feedback techniques that require access to the internal feedback loop of each power supply. This requires that the power supplies be designed for parallel operation. Also, some previously developed techniques require the use of one or more power diodes, such as Schottky diodes, for reliability. These power diodes collectively implement an “OR” function. Each power diode isolates a respective power supply in case a short circuit develops on the output terminal. In this case, the power diode may reverse bias and disconnects the associated circuit.